1. Field of the Invention
The present invention relates to an electromagnetic force driving device, and more specifically, to an electromagnetic force driving device, in which the size and weight can be reduced by combining a magnetic substance and a coil unit through a connection pin inside thereof, and electromagnetic characteristics and a holding force can be easily changed by forming independent motion paths.
2. Background of the Related Art
Generally, a circuit breaker is installed at a sending end or a receiving end of a power transmission line to open and close a normal current when there is no failure in a power system and, in addition, to protect the power system and various power devices (loads) by blocking a fault current when a failure such as a short circuit or the like occurs.
Such a circuit breaker is classified into a Vacuum Circuit Breaker (VCB), an Oil Circuit Breaker (OCB), a Gas Circuit Breaker (GCB) and the like according to an extinguishing/insulating material.
When the circuit breaker blocks the fault current, arcs generated between two contacting points should be extinguished, and the gas circuit breaker is classified again into a Puffer type, a Rotating arc type, a Thermal expansion type, a Hybrid extinction type and the like according to a method of extinguishing the arcs.
In such a circuit breaker, an opening operation should be accomplished at a high speed in order to block the failure current and promptly recover insulation between electrodes, and, for example, a high voltage/extra high voltage (generally, 365 kv or higher) circuit breaker for power transmission has a stroke length (SL) of about 250 mm and requires a force and a speed as large as to complete the operation within an extremely short time of 45 ms (milliseconds).
Although a hydraulic or pneumatic actuator is chiefly used as a high voltage/extra high voltage circuit breaker at present, there is a problem in that such an actuator is very expensive as much as one third of a total price of the circuit breaker, and, in Korean, most of actuators are imported.
Furthermore, in such a hydraulic or pneumatic actuator, working fluid may be leaked according to changes in the temperature of surrounding areas, and since the actuator is configured of a lot of parts, it is worried that the actuator may not operate if any one of the parts is out of order.
Accordingly, studies on development of actuators for substituting hydraulic or pneumatic actuators are under progress, and a spring actuator (a spiral spring), a motor drive (a system for converting a rotation motion into a linear motion using a motor), and a permanent magnetic actuator (PMA) are representatively used as results of the studies.
However, since the spring actuator is a system for obtaining power by releasing a compressed force when needed while a spring is compressed, its manufacturing cost is low. However, it is disadvantageous in that reliability of an operation state is low since elastic force of the spring is inconsistent. Therefore, it is difficult to apply the spring actuator to a high voltage/extra high voltage in which extinction gas should be sprayed, and, in addition, probability of failing the cutoff will be very high.
In addition, although manufacturing cost of the motor drive is low compared with that of the hydraulic or pneumatic actuator, since it is still expensive and difficult to generate a high power, the motor drive can be used for a low voltage, but may not exhibit sufficient performance at a high or extra high voltage.
In addition, the PMA actuator is formed to operate a mover using an electromagnetic force caused by a magnetic force generated by a permanent magnet and a magnetic field generated by flowing current through a coil, and since the PMA actuator is advantageous in that it has a simple structure and a good actuating efficiency and a consistent and uniform operation can be expected, it is frequently used as an actuator for a low voltage circuit breaker recently.
However, since the PMA actuator is a system which should be driven by a magnetic force generated by a permanent magnet and a magnetic force generated by flowing current through a coil, a path for flowing the magnetic field should be prepared using a magnetic substance (an iron core), and, in addition, the driven mover also should be formed of a magnetic substance.
Accordingly, when the breaking capacity is increased and thus the actuator needs a more powerful force, more magnetic fields should be generated, and the magnetic substance also should be increased as much as to flow the magnetic fields without being saturated, and thus the burden on the size of the actuator is increased, and since magnetic flux densities excited at the permanent magnet and the coil are inverse proportional to the square of an air gap length, there is a limit in applying the PMA actuator to a high voltage or extra high voltage circuit breaker having a large contact gap of a breaking unit, and thus there is a problem in that when the PMA actuator is used for an extra high voltage, its size should be much bigger, and its weight is much heavier than that of a hydraulic or pneumatic actuator, and, in addition, manufacturing cost is also increased.
Recently, an actuator such as an electromagnetic circuit breaker or an Electro-Magnetic Force Driving Actuator (EMFA) have been proposed in Korea Patent Registration No. 10-0718927 (title of the invention: Actuator using electromagnetic force and circuit breaker using thereof) to maximize the actuating speed and force while having a small size and weight to solve the problems of the circuit breakers.
Such an electromagnetic circuit breaker is a kind of circuit breaker having a structure of providing inner and outer hollow containers formed of a magnetic substance, arranging inner and outer permanent magnets on the facing surfaces of the inner and outer containers, and arranging a coil and a mover of a non-magnetic substance operating together with the coil as one piece between the inner permanent magnet and the outer permanent magnet, and thus when a current is supplied to the coil, the coil and the mover linearly move in the axis direction between the inner permanent magnet and the outer permanent magnet by an electromagnetic repulsion force generated by the magnetic field of the inner and outer permanent magnets and the current density of the coil.
However, in such an electromagnetic circuit breaker (EMFA), since the coil is arranged inside the enclosed outer container, it is difficult to connect an electric wire inside the outer container to supply current to the coil.
In addition, although the wire is connected, since the connected wire moves in the axis direction according to the linear motion of the coil, there is a problem of open circuit since the moving speed of the coil is too high and thus the electric wire is fatigued by compression and tension.
In addition, since a conventional electromagnetic circuit breaker has a mover arranged inside the enclosed hollow inner and outer containers, a moving axis or a connection axis should be extended long from the mover in the axis direction in order to connect the mover to an external movement element, and, in addition, the length of the extension should be long enough to sufficiently secure a stroke distance of the mover.
In addition, since increase of the length leads to increase of the overall height occupied by the circuit breaker, and the number of the connection axis or the moving axis should be increased or a connection axis or a moving axis of a large diameter should be used considering strength of the connection axis or the moving axis, there is a problem in that the overall weight of the circuit breaker is increased.
In addition, since the conventional circuit breaker has a coil unit and a magnetic substance formed in one piece, there is a problem in that electromagnetic characteristics and a holding force for maintaining a top or bottom dead point state cannot be changed according to an installation environment.